Hardening cobalt-nickel-chromium-iron alloys



Patented July 1, 1941 HABDENING COBALT-NICKEL-EHRQMEUM- IRON ALLOYSWilhelm Rohn, Hanan on the Main, Franz Bollenrath, Berlin-Johannisthal,and Heinrich Cornelius, Berlln-Adlershot, Germany No Drawing. Originalapplication December 24,

1938, Serial No. 247,696.

Divided and this application October 22, 1940, Serial No. 362,236. InGermany April v24, 1936 1 Claim. ((21.148-4) This application is adivision of our copending patent application Ser. No. 247,696, filedDec. 24, 1938.

This invention relates to a method of hardening certaincobalt-nickel-chromium-iron alloys having improved mechanical propertiesat elevated temperatures.

It is known that alloys which in addition to nickel as main constituentcontain alternatively proportions of chromium, molybdenum or tungsten aswell as on accasion iron, show a high creep resistance in hard rolledcondition at operating temperatures between about 400 and 600 C.

Investigations by the applicants have now led to the development ofalloys which on the one hand exhibit particularly high values of creepresistance at temperatures between 400 and 600 C. and which probably inthis range show the optimum with regard to strength at high temperaturesand which on the other hand still show also a high creep resistance athigher temperatures that is to say at temperatures up to and above 900C. Consequently they are for example suitable for the exhaust valves ofinternal combustion engines and exhaust turbines which operate in thetemperature range of 600 to 900 C.

The alloys according to this invention contain as main constituentscobalt and nickel in a total quantity of 50 to 70% the cobalt contentamounting to at least 10% and the nickel content amounting to at least0.05%. Tungsten and molybdenum may be present separately or together inamounts of from 0.05% up to 20%, for example from 2.5 to 15%, and thechromium content amounts to between 8 and 25%. In addition the alloysmay contain up to 30% of iron, for instance, from 0.5 to 30% of iron. Aparticularly good composition is 14 to 17% chromium, 14 to 16% iron, 5to 7% molybdenum, to. tungsten, to 27% (particularly 21%) of cobalt, andthe remainder essentially nickel apart from the usual deoxidising andmanufacturing additions, for example of manganese and silicon. Themanganese content may for example amount up to 1.5% and the siliconcontent up to 0.5%. If the alloys are to be used at temperatures abovetheir recrystallisation temperatures, the highest creep resistance isexhibited by the alloys stated when they have been annealed prior totheir use at temperatures exceeding the temperatures of use, for exampleat 1150 to 1300 C. If desired the alloys can also be employed in castcondition. If the alloys are to be used at temperatures below theirrecrystallisation temperatures the creep resistance may be increased byforging, rolling, drawing or hammering at the temperature between thetempera ture at which the alloys are to be used, and therecrystallisation temperature. method not only the creep resistance butespecially the elongation under the first loading ot'thc material isdecreased.

An alloy with about 16% chromium, about 15% iron, about 6% molybdenum,about 40% nickel and about 21% cobalt besides small proportions ofde-oxidising and manufacturing additions exceeds by about 10 to 15% asregards creep resistance in the temperature range 500 to 600 C, an alloyhitherto considered as particularly' good in this respect and consistingof 60% nickel, 15% chromium, 7% molybdenum and 18% iron. The advanceover the known alloys is clear it the creep limit as such is not takenfor comparison, but creep with time'which is frequently adopted forcomparison, that is to say the elongation per unit of time which a testpiece undergoes when loaded with a given weight at constant temperaturefor a long time.-

A comparative investigation about the creep resistance shows that therate of creep of the cobalt-containing alloys according to the inventionat constant temperature under a given load is only about one fifth toone tenth as compared with the abovementioned alloys of knowncomposition.

As a result of the considerable hardening which can be effected by coldworking the stem may be provided with a thin hardened surface layer byhammering, pressing, pressure polishing or pressure rolling and thusvaluable running properties under conditions of deficient lubricationobtained.

A further improvement, in particular as regards the resistance to creepat high temperatures, can be attained with the said alloys ii anaddition is made of one or more of the elements By this special.

thorium) or of metals of the first column 0! the 111th group of theperiodic system of elements (vanadium, eolumbium, tantalum). The amountsin which these elements may be contained in the alloy are as iollows:

sears seas:assessment; Mom 8%, Vanadium 15%. Columblum Tantalum Thelower limit of these additions ls generally not below 0.3% and the upperlimit of the additions together not above 15%. The alloys so modifiedcan be subjected tostill higher mechanical load at high temperatures,that is to say the mechanical properties at a given temperature arebetter than those of the alloys without .the apeciiied additions, or thetemperature at "which the alloys can stand a predetermined mechanicalload may be higher.

The above mentioned annealing at excessive temperatures before use forimproving the properties as regards creep limit at temperatures abovethe recrystallisation temperature, or the above mentioned 1orging,rolling, drawing, or hammering at temperatures between therecrystallisation temperature and the temperature particularly up to 5%atwhich thealloysaretobeused,iorthepurpose oi increasing the creepresistance at temperatures below the recrystallisation temperature andthe surface hardening by means oi cold working can also be applied tothe alloys with the additions of titanium, tantalum, columbium.vanadium, zirconium and thorium with good results. The composition ofthe alloys with the said additions so tar as the main constituents areconcerned. lies within the limits given above. Thus a particularlyadvantageous alloy can be obtained with about 15 to 27% cobalt, 14 to17% chromium, 6 to 16% iron, 5 to 7% molybdenum, 0 to 7% tungsten,especially 3 to 7% tungsten, besides nickels also main constituents,with additions of up to 5% titanium, up to 15% tantalum, up to 15%columbium, up to 8% thorium, and possibly the usual deoxidising andmanuiacturing additions.

We claim:

Method of hardening an alloy consisting of from 14 to 17% chromium, 14to 16% iron, 5 to 7% molybdenum, 0.05 to 7% tungsten, 15 to 27% cobalt,and 52 to 27% nickel, which method consists in cold working the saidalloy.

WILHELM ROHIN'. HEINRICH CORNELIUS. FRANZ BOLLENRATH;

